Berkshire Hathaway is controlled by Warren Buffett, who is chairman and chief executive of the company which owns a range of companies, including GEICO and NetJets, a substantial stake in Heinz, and has stakes in American Express, Procter & Gamble and IBM. The company is noted for outperforming the stock market under the leadership of Buffett, a value investor.

Amid the buzz last month around the arrival in China of Warren Buffett and Bill Gates, one person seems to have slipped by largely unnoticed: Li Lu , one of the student leaders during the Tiananmen Square protests in 1989 who is still on the central government's wanted list.

Li, now a highly successful hedge fund manager in the US and, according to some, the chosen successor to Buffett at Berkshire Hathaway, has been banned from entering China since fleeing to France and then the United States following the government crackdown in 1989.

However, Li was part of Buffett's entourage when he visited Shenzhen for the first time for a recent BYD shareholders convention.

An employee at Himalaya Capital, Li's US hedge fund, confirmed his presence in Shenzhen, but Li was unavailable for comment on the details of the visit or visa arrangement with the central government.

Leaked government directives to state media, confirmed Li's presence, with a directive from the Guangdong provincial propaganda bureau telling mainland journalists attending the BYD stockholders convention that they were 'only allowed to take pictures of Warren Buffett, and not of Li Lu'.

Security during the convention was extremely tight, and foreign media were barred from attending.

Li, who is credited with introducing Buffett to automaker BYD, and who himself owns a 2.5 per cent share of the company, according The Wall Street Journal, spent several years at New York's Columbia University after fleeing China, learning English and simultaneously earning degrees in economics, law and a graduate degree in business, before beginning his career in finance.

While the ban on Li entering the mainland is said to have been occasionally lifted in recent years for short business trips, the government directive to the media for this latest visit shows the sensitivity that still surrounds those involved in the 1989 student protests.

The Guangdong propaganda directive sent out to local media said the government had told Li he could not make himself 'highly visible'.

Professor Jiang Wenran , from the China Institute at the University of Alberta, Canada, said: 'Over the years the Chinese government seems to have developed a policy that if members of the student movement of 1989 are not still active they are more or less left alone.'

Despite this, the central government seems to be adopting a cautious attitude towards Li, who remains on the wanted list.

'Li is an important person, he might be running one of the biggest investment companies in the world in a few years,' Jiang said. 'China doesn't want to miss out on the huge economic opportunities but at the same time they don't want to make it a triumphant return with the media present, which is why we have the current awkward arrangement.'

Sebastian Veg, a former researcher at the French Centre for Research on Contemporary China in Hong Kong, said: 'The fact that Warren Buffett brought him along speaks to the clout business leaders enjoy in China.

'It is quite difficult to imagine a senior politician demanding to be accompanied by a former dissident on an official trip to China.'

A Hong Kong media report said Li entered on a US passport with a special visa, having receiving permission from the central government.

'If this model applies to Li then it would be interesting to see if it applied to the other former student leaders from 1989,' Jiang said.

'We can only speculate what would happen if Chai Ling tried to come back to do business since she is not as important as Li.'

Chai, known as the 'commander-in-chief' during the student protests, runs a US-based higher education software company, which she founded with her husband.

In the lead-up to the much-publicised visit by Gates and Buffett, state media were also banned from writing anything negative about Chen Guangbiao , the recycling billionaire who pledged to give all of his money to charity.

Chen is one of the few mainland billionaires to have answered Gates' and Buffett's call to philanthropy.